As the general contact structure for the above-mentioned switch, the structure as shown in FIG. 20 has been known.
Specifically between the inner space are a switch cover 201 and a switch base 202 oppositely arranged from to each other vertically, an upper terminal 203 and a lower terminal 204 are oppositely arranged one above the other with a predetermined gap, and contacts 205, 206 are secured to the opposing faces of both of the terminals 203, 204 respectively.
A common terminal 207 is disposed vertically on one side of the contacts 205, 206, in which the base end of a first movable member 208 is engaged to the lower portion of the common terminal 207 while the free end of the first movable member 208 is situated in the vicinity of the contacts 205, 206 of the above-mentioned upper and lower terminals 203, 204.
A second movable member 209 inserted between the contacts 205, 206 is engaged at one end thereof to the free end of the first movable member 208, and the second movable member 209 has contacts 210, 210 secured at the positions corresponding to the contacts 205, 206 respectively. Further, a spring 211 is stretched between the outer end of the second movable member 209 and the common terminal 207, so that the contact 210 on the second movable member 209 is always biased to be in contact with the contact 206 on the lower terminal 204.
An operation member 212 undergoing the depressing operation is supported above the free end of the second movable member 209. When the operation member 212 is depressed, the free end of the second movable member 209 moves downwardly to switch the contact 210 of the second movable member 209 from the contact 206 on the lower terminal 204 to the contact 205 on the upper terminal 203.
The contact structures having been constituted as described above have the following problems.
Namely, upon switching the second movable member 209, the second movable member 209 is slanted largely corresponding to the amount of depression of the operation member 212 to result in a slip, due to the slanting, between the contact 210 of the second movable member 209 and the contact 206 on the lower terminal 204 in a partially contacted state, as well as a similar slippage for the contact between the contact 205 on the upper terminal 203 and the contact 210 of the second movable member 205 after switching operation.
If the slipping contact is acted between the contacts 206, 210 and between the contacts 205, 210, the contact faces are abraded to roughen the contact faces thereby resulting in malcontact, reduction in the switch operation characteristic and, thus, reduction in the switch life.